This invention relates to mass flow measurement devices, that is to say, devices which measure the mass of fluid which is flowing passed a particular point. Devices of this kind find particular application for example, in circumstances where precise amounts of liquid or gaseous fuels are to be metered. Because the density of the fluid may not be constant, it is often not sufficient merely to monitor the volume of fluid passing a particular point. The present invention seeks to provide an improved mass flow measurement device.